The present invention relates to high surface area chromium oxides and hydroxides of valence state III useful as catalysts for a variety of processes including fluorination.
Aerogels of various metal oxides have been prepared by hydrolysis of alkoxides of silicon, aluminum, magnesium, and certain other metals whose alkoxides are soluble in lower alcohols, followed by hypercritical removal of solvent. Chromium(III) does not have readily available alkoxides suitable for this use. Nevertheless, chromium(III) oxide and hydroxide (generally referred to as chromia) are used for a variety of catalytic processes where increased surface area might improve activity. Available chromia catalysts generally have surface areas (by the BET technique) no greater than 350 m.sup.2 /g and frequently less than 250 m.sup.2 /g. See, for example, R. L. Burwell Jr. et al., Am. Chem. Soc. 58, 697 (1936), and R. L. Burwell Jr. et al., Am. Chem. Soc. 82, 6272 (1960).
Chromium(III) oxide catalysts for the fluorination of chlorinated hydrocarbons by HF are disclosed in U.S. Pat. Nos. 3,258,500 (to Swamer et al.) and 3,978,145 (to Knaak). The former discloses a preferred gel-type catalyst produced by reducing chromium(VI) oxide with ethanol in water, drying the gel and activating in an inert atmosphere at 400.degree.-600.degree. C. The latter discloses a chromium(III) oxide gel-type catalyst hydrated with water at elevated temperatures before use.